1. Field
The embodiment(s) discussed herein are related to storage apparatus including a magnetic storage medium having a structure where recording tracks are divided by providing grooves or nonmagnetic regions in a data recording surface, or a magnetic storage medium formed with isolated magnetic dots in a user data portion.
2. Description of the Related Art
In recent years, as techniques for enlarging a recording capacity by enhancing the areal recording density of a magnetic storage medium in a hard disk drive, there have been a perpendicular magnetic recording technique where the storage medium is magnetized in the depth direction thereof, and a medium technique where predetermined concave and convex patterns are formed in the perpendicular magnetic storage medium and where data signals and servo signals (signals which are used for a head to trace tracks) are recorded in the convex patterns. The perpendicular magnetic storage medium to which the prepatterned medium technique is applied, is called a “discrete track medium (DTM)”.
The DTM has the regions of nonmagnetic parts between recording tracks to reduce the interferences between the tracks. Further, it is expected to introduce a recording technique which employs a medium called a “bit patterned medium (BPM)” where the tracks in the DTM is divided by nonmagnetic parts so as to form isolated magnetic dots in a track direction on the disk medium and where the magnetic dots are used as information units (bits).
It is considered that the servo patterns of the magnetic disk apparatus employing such a BPM technique are formed in terms of the presence or absence of magnetic regions by working a magnetic recording layer (magnetic region). In this case, the magnetization state of the servo pattern portion is usually such that the direction of the magnetization is either an upward toward the front surface side of the medium or a downward contrary thereto. Besides, in the servo pattern portion, the pattern is made long in order to ensure servo signal quality. Therefore, the area (volume) of a magnetic material pattern in the servo pattern portion is considerably larger as compared with the area (volume) of the dot serving as the information unit in a data portion.
In the servo pattern portion, therefore, the influence of magnetostatic interactions becomes intense, and the deterioration of the signal attributed to a thermal fluctuation is more liable to occur than in the user data portion. In addition, once the servo signal is recorded in the magnetic material pattern of the servo pattern portion, it is not recorded again. As a result, the magnetization state of the magnetic material pattern of the servo pattern portion becomes unstable against heat, and poses a problem in that the track positioning precision of the magnetic head worsens. Regarding this problem, it is proposed in Japanese Laid-Open Patent Publication No. 2006-66006 that a servo pattern is re-magnetized after detecting the lowering of the reproduced output of the servo signal.
However, a state where the lowering of the servo signal has occurred in the detection of the reproduced output, is a state where the positioning precision of the head to the track has been deteriorated, that is, a state where the positioning precision of the head to a region for the re-magnetization has been deteriorated. When the decision of the lowering of the servo signal is made stricter in order to better the positioning precision, the re-magnetizations are frequently performed with the technique disclosed in Japanese Laid-Open Patent Publication No. 2006-66006. This can cause the problems that the re-magnetization is required during the use of the disk apparatus by a user, and that a re-magnetization process becomes long to increase power consumption.